Hi Ian,
I tried to merge both go files as you suggested and it is showing same
error as the previous one.
Following is the code. Also, I would like to mention that I am using Go1.15
linux/amd64.
*$CGO_ENABLED=1 go build .*
*# _/home/ami.ladani/Downloads/experiment./main.go:22:44: baz_ptr.b
undefined (type *GoBaz has no field or method b)./main.go:23:44: baz_ptr.f
undefined (type *GoBaz has no field or method f)*
// c_header.h
typedef void (*cb)(void* qux, int status, void *command_data, void
*cb_data);
typedef struct{
int a;
int b;
} Foo;
typedef struct{
char* ch;
cb callback;
} Bar;
typedef struct{
Foo* f;
Bar* b;
} Baz;
Baz* allocateBaz(){
Baz* baz = malloc(sizeof(Baz));
Bar* bar = malloc(sizeof(Bar));
Foo* foo = malloc(sizeof(Foo));
baz->f = foo;
baz->b = bar;
return baz;
}
//main.go
package main
/*
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include "c_header.h"
*/
import "C"
import "unsafe"
type GoBaz C.struct_Baz
type GoBar C.struct_Bar
type GoFoo C.struct_Foo
func main() {
baz_ptr := (*GoBaz)(unsafe.Pointer(C.allocateBaz()))
bar_ptr := (*GoBar)(unsafe.Pointer(baz_ptr.b))
foo_ptr := (*GoFoo)(unsafe.Pointer(baz_ptr.f))
}
Thanks!
Ami
On Friday, July 23, 2021 at 3:43:19 AM UTC+5:30 Ian Lance Taylor wrote:
> On Thu, Jul 22, 2021 at 2:53 PM Ami Ladani <amila...@gmail.com> wrote:
> >
> > I am trying to access members of a C struct from go. Compiler is showing
> structure's members are undefined. I have attached my code and the error
> message below.
> >
> > Please have a look and help if you can.
> >
> > $CGO_ENABLED=1 go run main.go cfuncs.go
> > # command-line-arguments
> > ./main.go:18:44: baz_ptr.b undefined (type *GoBaz has no field or method
> b)
> > ./main.go:19:44: baz_ptr.f undefined (type *GoBaz has no field or method
> f)
> >
> > //c_header.h
> > typedef void (*cb)(void* qux, int status, void *command_data, void
> *cb_data);
> > typedef struct{
> > int a;
> > int b;
> > } Foo;
> >
> > typedef struct{
> > char* ch;
> > cb callback;
> > } Bar;
> >
> > typedef struct{
> > Foo* f;
> > Bar* b;
> > } Baz;
> > //--------------------------------
> >
> > //cfuncs.go
> > package main
> > /*
> > #include<c_header.h>
> > #include <stdlib.h>
> >
> > Baz* allocateBaz(){
> > Baz* baz = malloc(sizeof(Baz));
> > Bar* bar = malloc(sizeof(Bar));
> > Foo* foo = malloc(sizeof(Foo));
> > baz->f = foo;
> > baz->b = bar;
> > return baz;
> > }
> > */
> > import "C"
> > //-------------------------------------------------
> >
> > //main.go
> > package main/*
> > #include<c_header.h>
> > extern Baz* allocateBaz();
> > */
> > import "C"
> > import "unsafe"
> > type GoBaz C.struct_Baz
> > type GoBar C.struct_Bar
> > type GoFoo C.struct_Foo
> > func main() {
> > baz_ptr := (*GoBaz)(unsafe.Pointer(C.allocateBaz()))
> > bar_ptr := (*GoBar)(unsafe.Pointer(baz_ptr.b))
> > foo_ptr := (*GoFoo)(unsafe.Pointer(foo_ptr.f))
> > }
> > //--------------------------------
>
>
> Interesting. I think that has to do with the fact that you are using
> two different Go files that both #include <c_header.h>. <c_header.h>
> uses typedef to define anonymous structs. The fact that the header is
> being included twice in the same package seems to be causing cgo to
> generate two different Go structs, one for each .go file. And then it
> can't figure out the definition of the Go struct, so you get this
> error.
>
> This is probably a bug in cgo, so feel free to file an issue at
> https://golang.org/issue.
>
> You can probably make progress by combining the .go files so that you
> only have a single import "C" with a #include <c_header.h>.
>
> Ian
>
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